problem in blender, help!

wow, im starting to use this site more and more now, anyways the communitys great. i have a problem. in blender for ubuntu 11.04 im trying to make a gun that shoots, ive found plenty of tutorials online on how to do it, but when i press p to play, all the bullet does is appear and fall. and incase your wondering, yes. i set the y-axis to 100, and its logic is set to dynamic, please help.